Evaluation of vertical impact factor coefficients for continuous and integral railway bridges under high-speed moving loads

In the railway bridge analysis and design method, dynamic train loads are regarded as static loads enhanced by an impact factor (IF). The IF coefficients for various railway bridges have been reported as a function of span length or frequency of the bridges in Eurocode (2003). However, these IF coefficient values neglect the effects of very high speeds (>200 km/h) and soil-structure interaction (SSI). In this work, a comprehensive study to assess the impact factor coefficients of mid-span vertical displacements for continuous and integral railway bridges subjected to high-speed moving loads is reported. Three different configurations, each for the three-dimensional (3D) continuous and integral bridge, are considered. Also, single-track (1-T) and two-track (2-T) “real train” loading cases for both these bridge types are considered. Subsequently, finite element analysis of the full-scale 3D bridge models, to identify their IF values, considering the effects of SSI for three different soil conditions, is conducted. The IF values obtained from the study for both bridge types are comparable and are greater than the values recommended by Eurocode (2003). The results reveal that with a loss of soil stiffness, the IF value reduces; thus, it confirms the importance of SSI analysis.